High speed printer with leaflike impact means

ABSTRACT

A printing hammer with a lesser length damper in juxtapositional relationship, which damper provides vibration damping of the printing hammer. High speed line printers utilizing impact printing means are often limited to a maximum speed due to the spring response and continued vibration of the printing hammers. The printing hammer taught by the instant invention incorporates a lesser length damper in juxtapositional relationship to provide vibration damping by having the damper vibrate at a natural frequency different from that of the printing hammer. During the actuation of the printing hammer, the mass of both the printing hammer and the damper strike the print surface. Subsequently, the printing hammer and the damper will vibrate in opposition to one another to rapidly effect a damping action. A damper length which is approximately 0.707 times the length of the printing hammer provides the damper with a natural frequency twice that of the printing hammer. Other means for providing differing vibration frequencies are anticipated.

United States Patent Rose [ Oct. 30, 1973 HIGH SPEED PRINTER WITHLEAFLIKE IMPACT MEANS Primary Examiner-Robert E. Pulfrey AssistantExaminerE. M. Coven Attorney-William C. Cahill et a1.

[57] ABSTRACT A printing hammer with a lesser length damper injuxtapositional relationship, which damper provides vibration damping ofthe printing hammer. High speed line printers utilizing impact printingmeans are often limited to a maximum speed due to the spring responseand continued vibration of the printing hammers. The printing hammertaught by the instant invention incorporates a lesser length damper injuxtapositional relationship to provide vibration damping by having thedamper vibrate at a natural frequency different from that of theprinting hammer. During the actuation of the printing hammer, the massof both the printing hammer and the damper strike the print surface.Subsequently, the printing hammer and the damper will vibrate inopposition to one another to rapidly effect a damping action. A damperlength which is approximately 0.707 times the length of the printinghammer provides the damper with a natural frequency twice that of theprinting hammer. Other means for providing differing vibrationfrequencies are anticipated.

2 Claims, 4 Drawing Figures HIGH SPEED PRINTER WITH LEAFLIKE IMPACTMEANS This application includes an improvement of the line printerdescribed in the co-pending US. Pat. application entitled Impact LinePrinter, Ser. No. 97,166, filed Dec. ll, 1970.

The present invention pertains to hammers especially suited for lineprinters utilizing impact as a means for printing' Line printerssimultaneously form a line of characters and are generally high speeddevices (500 lines or more per minute). These high speed printers, suchas taught in the co-pending patent application entitled Impact LinePrinter, are mechanically capable of actuating the hammers to becommensurate with communication line information speeds (1,200 Baud andup). A limiting factor in increasing the pringing speed and yet obtain aclear copy is associated with the structure and operation of the hammeritself.

A primary object of the present invention is to provide a vibrationdamped impact printing hammer which does not damp the initial impactforce.

Another object of the present invention is to provide a damped impactprinting hammer which prevents multiple print impressions and ghosting.

Another object of the present invention is to provide a damped impactprinting hammer which is commensurate with the speed of high speed lineprinters.

Still another object of the present invention is to provide a dampedimpact hammer which may be used in existing line printers.

These and other objects of the present invention will become apparent tothose skilled in the art as the description thereof proceeds.

The present invention may be described by reference to the accompanyingdrawings, in which:

FIG. 1 illustrates a cross-sectional view of the damped hammer and therelated apparatus.

FIG. 2 illustrates a portion of the paper feed mechanism andrelationship of the paper to the hammers and ribbon.

FIG. 3 illustrates the relationship between the hammer and hammersupport and the frame of the printer.

FIG. 4 illustrates a typical character printed by the system of thepresent invention.

Referring to FIGS. 1-3, a plurality of hammer units 1 are aligned witheach other and are mounted in a hammer support 2. In the embodimentchosen for illustration, the hammer units 1 are mounted in the support 2by clamping the respective hammer units 1 between opposed faces ofclamping bars 3 and 4, the latter being an extension of support 2. Thehammers 5 of hammer unit 1 are formed from appropriate steel to providethe facility to be drawn away from the paper surface, to be released,and to snap forward to strike the paper and return to its originalposition. The hammers may also be stamped from a single sheet of metalwith each of the individual hammers forming fingers in comb-like fashionfrom a base which is clamped between clamping bars 3 and 4. Each of thehammers 5 is provided at the upper portion thereof with a strikingsurface 6 that comprises a rectilinear edge extending perpendicularlytoward the platen when the hammer unit 1 is mounted in the printer. Theutilization of an edge as the striking surface 6 facilitates theproduction of dots or marks in the matrix of a character, as will bedescribed more completely hereinafter. Adjacent each hammer 5 is adamper 7 also mounted in support 2 by clamping bars 3 and 4. The lengthand weight of damper 7 should be designed such that damper 7 will have anatural frequency of vibration different from that of the hammer 5 inaccordance with the laws of vibration of elastic bodies.

A platen 37 comprises a horizontally extending edge functioning as astriking surface. The platen 37 is gripped in a clamp 8 and is held in aposition opposite to the striking surface 6 of the respective hammerunit 1. Flexible sheet material 9, such as paper, upon which charactersare to be formed is fed through the printer as shown in FIG. 2 on a pairof sprockets 10, ll engaging sprocket holes 12 provided in the paper. Aconventional ink ribbon I3 is wound about a feed roll 14 and passes overguides 15 and 16 to a take-up roll 17.

Electromagnets 18 are provided for each of the hammer units 1. Onenergizing the electromagnet coil, both the hammer 5 and damper 7 aredeflected toward the pole face 19, 19. The distance between the platenedge and hammer 5 when the latter is in the quiescent v'ertical positionis such that the striking face 6 of the hammer 5 will strike the platenedge during the first half of the vibratory cycle after the hammer 5 isreleased from the influence of the energized coil 18. When theelectromagnet coils is de-energized, the magnetic field collapses,permitting both the hammer 5 and the damper 7 to travel toward the paper9 and the platen 37. After the hammmer 5 strikes the paper 9 and platen37, it will rebound and continue to vibrate with decreasing amplitudeuntil the energy stored therein has been dissipated.

If the length and/or weight of the hammer 5 and the damper 7 aredifferent from each other, and not related by odd harmonics of oneanother, the vibration of one will interfere with the vibration of theother. If the cross section and material of the hammer 5 and the damper7 are the same and their lengths are in the ratio of approximately 1 to707, respectively, the frequency of vibration of the first is half thatof the latter, causing each to interfere with the other. Each time thevibratory movement of one interferes with the vibratory movement of theother, an impact will occur. Each of these impacts will necessarilydissipate energy from the hammer 5, causing its vibratory amplitude todecrease rapidly. Thereby, the total vibration time of the hammer 5 issubstantially reduced and the hammer is clamped.

A second function performed by the damper 7 is that of contributing itsspring force to that of the hammer 5 to aid in accelerating the hammer 5away from the pole face l9, l9 and toward the platen 9. By carefuldesign, it is possible to reduce the mass of the hammer 5 to lighten thehammer assembly without jeopardizing the capability of the hammer 5 instriking the platen 37 as the hammer spring force required inconjunction with the damper 7 is less than if the damper 7 were notpresent.

A third function performed by the damper 7 is that of providingadditional iron in the coil flux path during coil energization. Thispermits a more efficient use of the available flux. Further, theadditional iron permits a greater displacement and/or misalignmentbetween the hammer 5 and the electromagnet 18 without impairment ordegradation of the printing operation.

The face 19 of the electromagnet 18 may be displaced from a verticalline such that it parallels the center line of the hammer unit 1 whenthe latter has been attracted toward the energized electromagnet 18. Aportion of coil face 19' may be raised toward the hammer unit 1 suchthat the profile of the coil face matches the profile of the damper 7and the extended portion of hammer 5 comprising hammer unit 1. Such adesign feature will aid in uniformly attracting the hammer unit 1 to theelectromagnet 18.

The electromagnets 18, each co-operating with one hammer unit 1, may bemounted onto the frame 21 of the printer if it is desired that theyremain stationary.

The hammer support 2 is also secured to the frame 21 but is mounted topermit horizontal reciprocal stepping. The movable mounting is providedby a plurality of two-dimensional semi-flexible straps 22 clamped at oneend thereof to an upright 23 extending from the hammer support 2. Asshown in FIG. 3, the opposite ends of the straps 22 are attached to theframe 21. Each of the straps 22 is made of spring steel which permitstwo-dimensional flexure perpendicular to the face of the strap whileinhibiting flexure in any other direction. The mounting of the hammersupport 2 in this fashion securely fixes the hammer units 1 at apredetermined vertical position while nevertheless permitting the hammersupport 2 and hammer units 1 to be moved laterally of the paper 9. Thislateral movement is indicated in FIG. 3 by the arrow 24. Lateral motionis imparted to the hammer support 2 and hammer units 1 by a steppingmotor 25 connected to the hammer support 2 by a two-dimensionally,semi-flexible strap 26. While other means may be utilized to connect thehammer support 2 to the stepping motor 25, the strap 26 readilytranslates the rotary motion of the stepping motor shaft 27 intorectilinear motion and permits the stepping action of the motor 25 tosimply and positively step the hammer support 2 and hammer units 1.

The stepping motor 25 is reversible and is stepped to a number of steppositions corresponding to the number of horizontal dot or markpositions in the matrix forming a character. A mechanical stop 28 may beprovided to engage the clamp extension 29 secured to the motor shaft 27.

The paper 9 is advanced through the utilization of a second steppingmotor 30 which is connected through gears 31 and 32 to sprockets l and11. The selected energization of stepping motors 25 and 30 combined withthe energization of appropriate electromagnets l8 generate a matrix ofstep positions for the formation of characters.

The operation of the printer of the present invention may now bedescribed with the aid of FIG. 4. In FIG. 4, a characer 7 is shown andis formed by the selective printing of marks or dots in a matrix. In theembodiment chosen for illustration, a seven by eight matrix has beenchosen; it will be obvious to those skilled in the art that a greater orlesser number of step positions may be utilized in accordance with therequirements of the specific application.

Referring to FIG. 4, the horizontal or lateral step positions aredesignated step positions x1, x2, x7, while the vertical step positionshave been designated yl, y2, y8. Assuming that the character 7 is to beprinted, the paper 9 will be stationary and dot or mark position x1, y8will be between the striking surface of the platen 37 and the hammerunit 1. The electromagnet 18 will be energized and subsequentlydeenergized, causing the hammer to be drawn away from the paper 9 andthen released. The momentum of the hammer 5 will cause it to strike theribbon 13 and force it against the paper 9 and both the paper and ribbonagainst the platen 37. Since the striking surface 6 of the hammer 5 isoriented at right angles to the edge of the platen 37, a relativelysmall mark or dot 33 will be formed. The stepper motor 25 will then beenergized and the hammer unit 1 moved to the horizontal step positionx2. The electromagnet 18 will again be energized and the hammer 5 andplaten 37 will form the mark 34 in position x2, y8. The stepping motor25 will continue to step, causing the hammer support 2 and hammer units1 to step to successive step positions until the hammer unit 1 reacheshorizontal step position x7. After the mark is printed at that position,the stepping motor 30 will be energized, causing the paper 9 to beslightly advanced. Vertical step position y7 is now aligned between thestriking surface of the hammer units and platen. The stepping motor 25will again be energized in the reverse direction, causing the hammerunits 1 to step to the left as shown in FIG. 4 with the hammer units 1being energized at the appropriate step positions for the formulation ofthe character 7. The hammer units 1 therefore continue to step back andforth laterally or horizontally across the paper 9 with theelectromagnet 18 associated with the hammer unit 1 energized at theappropriate time. At the end of each horizontal sweep from left to rightor right to left, the paper 9 is advanced or stepped to bring the nextrow of mark positions in the matrix into striking position between thehammer units 1 and platen 37. It may be noted that only oneelectromagnet energizes a given hammer unit, regardless of the hammerunit position; thus, while the hammer support 2 and hammer units 1 arestepped or oscillated back and forth, the electromagnets 18 associatedwith each hammer unit 1 remain stationary. While the hammer units 1 arethen sometimes slightly misaligned with their correspondingelectromagnets, they nevertheless remain within the area of influence ofthat electromagnet to the extent that the hammer unit 1 is actuated bythe energization and deenergization of its corresponding electromagnet.Since the electromagnets 18 remain stationary, the mass that isaccelerated and decelerated during the stepping action of the hammerunits 1 is greatly reduced and the speed with which the hammer units maybe stepped is increased correspondingly. The use of the semi-flexiblestraps 22 greatly reduces friction that otherwise would occur if thehammer support 2 were guided by more conventional means, such asrollers, sliding guides, etc. Further, the tolerances are veryinexpensively but accurately maintained through the utilization of thestraps 22. Similarly, the strap 26 used by transmitting the steppingmotion to the hammer units eliminates problems that otherwise wouldoccur with more conventional motion transmitting media, such as theimprecision of chain drives or the backlash of rack and pinions.

I claim:

1. In a printer for printing characters by an impact printing technique,the improvement comprising: a plurality of cantilevered fingersextending from a base and forming impact hammers, each including a flatsurface extending substantially its entire length and each formed frommagnetically attractable material and having a length to provide apredetermined natural vibratory frequency; a plurality of cantileveredfingers exfrequency; a plurality of electromagnets, each positionedadjacent a different one of said hammers to attract, when energized, theadjacent hammer and damper in contact with said adjacent hammer.

2. The combination set forth in claim 1, wherein each of said dampers isapproximately 0.707 times the length of said dampers.

1. In a printer for printing characters by an impact printing technique,the improvement comprising: a plurality of cantilevered fingersextending from a base and forming impact hammers, each including a flatsurface extending substantially its entire length and each formed frommagnetically attractable material and having a length to provide apredetermined natural vibratory frequency; a plurality of cantileveredfingers extending from said base and forming dampers of magneticallyattractable material, each damper including a flat surface extending itsentire length, the flat surface of each damper contacting the flatsurface of a different one of said hammers throughout the length of saiddamper, clamping means clamping each damper in contact with a differentone of said hammers at said base, said dampers having a length toprovide a natural vibratory frequency different from said predeterminedfrequency; a plurality Of electromagnets, each positioned adjacent adifferent one of said hammers to attract, when energized, the adjacenthammer and damper in contact with said adjacent hammer.
 2. Thecombination set forth in claim 1, wherein each of said dampers isapproximately 0.707 times the length of said dampers.